Process for centrifugal separation



Patented Nov. 3, 1953 PROCESS FOR CENTRIFUGAL SEPARATION OF UREACOMPLEXES FROM ORGANIC MIXTURES George B. Arnold, Glenham, and LouisKovach, Beacon, N. Y., assignors to The Texas Company, New York, N. Y.,a corporation of Delaware No Drawing. Application November 30, 1949,Serial No. 130,338

5 Claims.

This invention relates to the formation of urea complexes and to theseparation of urea complexes from mixtures of organic compounds. Moreparticularly, this invention discloses a method for separating ureacomplexes from mixtures of organic compounds by centrifugal means.

This invention involves the discovery that a temperature between 120 and140 F. should be maintained during the centrifugal separation ofcomplexes which are formed by contact of a mixture of organic compoundswith an aqueous solution or slurry of urea. It is essential to maintainthe specified critical temperature range during centrifugal separationin order to effect clean cut separation of the two phase liquid mixturecomprising aqueous slurry of urea complex and organic compounds. Whenthe centrifugal separation is eifected at temperature between 120 and140 F. there is obtained a light stream comprising mainly organiccompounds and a dense stream comprising an aqueous slurry of ureacomplex.

It has recently been discovered that urea forms a solid complex withcertain types of organic compound. The class of compounds which complexwith urea comprises normal aliphatic hydrocarbons containing at leastsix carbon atoms, terminal-substituted normal aliphatic hydrocarbonscontaining at least six carbon atoms, such as n-decanol andn-dodecylbenzene and some methyl-substituted n-aliphatic hydrocarbons.This discovery provides a very useful tool in the resolution of organicmixtures, such as petroleum fractions and the oil product obtained bycatalytic conversion of carbon monoxide and hydrogen. Urea complexing isuseful both in the isolation of specific compounds, and in the removalof undesirable components from a petroleum fraction. The isolation ofstraight chain olefins from synthetic gasoline and synthetic gas oilillustrates the utility of urea com- 'plexing in the isolation ofparticular compounds from mixtures. Normal olefins, particularlyalpha-olefins which predominate in synthetic fuel, are valuablechemicals and are in demand as starting materials for the 0x0 reaction,and as intermediates in the preparation of synthetic detergents andlubricant additives. Dewaxing of petroleum fractions such as gas oil andlubrieating oils to produce low pour products illustrates the employmentof urea complexing to free a petroleum fraction of undesirableconstituents. The main commercial usefulness of urea complexing at thepresent time lies in the dewaxing of gas oils and other petroleumfractions; low pour diesel fuel is in demand as a jet fuel and for coldweather operation of diesel engines; refrigerator oils characterized bylow pour and Freon haze test are required in air-conditioning andrefrigeration equipment.

Various procedures have been proposed for effecting formation of ureacomplexes with organic compounds. It has been proposed that complexformation be effected by contacting an organic mixture with a saturatedor supersaturated solution of urea in a polar solvent, such as aliphaticalcohols, aliphatic ketones, water, etc. Complex formation is alsoeffected by contacting an organic mixture with a slurry of urea in apolar solvent. Complex formation is also effected by contacting anorganic mixture with a fixed bed of urea; in procedures of this sort theurea is advantageously used in conjunction with a particulate solid,such as Filter Cel, alumina, silica, sand, etc. In all these varioustechniques for effecting complex formation the presence of a polarcompound, such as water, an aliphatic alcohol or an aliphatic ketoneexpedites complex formation.

Urea complexes are decomposed at elevated temperature over 160 F. and asa matter of fact, substantial decomposition occurs at temperatures over140 F. Accordingly, complex formation is efiected at temperaturesbetween 0 and 150 F. and preferably at temperatures between 80 and 140F. at which no refrigeration is required. Atmospheric temperature hasbeen found to be a convenient, effective temperature at which to contacturea with a mixture of organic compounds. Apparently, complex formationis not critical to pressure so that pressures ranging fromsub-atmospheric to super-atmospheric pressures up to and above 20atmospheres may be employed. However, atmospheric pressure is ordinarilyused to effect complex formation.

The discovery that urea complex formation can be effected by contact ofan organic mixture with an aqueous solution or slurry of urea hasresulted in substantial economies in the application of urea complexingto commercial operations. The aqueous solution is readily separated fromthe organic mixture and moreover, residual water is simply removed fromthe organic mixture so that contamination of organic mixture, such asdewaxed gas oil, is obviated. The aqueous solution employed for ureacomplexing should be substantially saturated and is preferablysuper-saturated or an aqueous slurry or urea. Diluteagueoussolu-tionstare noheftective-joncom- Dlex formation "because thecomplex is dedoim posed by the extra dissolving power of a diluteaqueous urea solution. Aqueous solutions or aqueous slurries are mainlyemployed in forming complexes with lower molecular 'wejgnt sucha5n-aliphatic hydrocarbons; the dewaxing of gas oils illustrates such ause. However, urea in aqueous solution or slurry ,is'ialso 118.611 inthe dewaxing of heavier oil stocks.

A plurality of methods have been proposed for separating the complexfrom the mixture .of organic compounds. Simple decantatioii',ifiltration and centrifugal separators are the means ordinarily employedto separate the complex from the organic mixture. This invention,howcxcx, co cerned solely wi h the separation of omplex fr m th or animix ure by means of centrifugal separations.- Moreover, this inventionisrfurther limited to c ntrifu l sep a io of complex fr m -.a immunewherein omp ioxmation results from onta of an r ni mixtnrewvith anaqueous saturated solution or queous slurry of :urea.

We have discovered that centrifugal sonar ration oianreacomplex i omsmix ur comp i ing water, organic mixture and; solid complex 'resultinzi-romoontactofan.or anicrnixtu e-'wi h an aqueous solution or slurry ofurea. can onl he. effected within a very sm ll criti al temp r aturerange of 120 and 1510? F. If the centrifuge is operated at temnera resbove .1510 ubstantial complex d comn tiono cur Attemneratures .below 120F- compl x isdcp i d n thesurface of ithe centrifu ebowlwith subsequentc g ing of en ifu When h mperature is maintainedbetween 120 and 140 F.odouring .centrifugal ;separation, the aqueous-phase is denser than :thecomplex and acts as a carrier lthGIGfOK. According y} the temperaturemust :be

-maintained:between .120and 14D" durin Separation of urea complex fromainiatureieompllia ing organic layer, aqueous phase and solid ureacomplex.

lnlefiecting centrifugal-separation urea-room plex in accordancewitlritheuprocessnf this invention, it is advisable :to effect:formationzof .the .complex: within the same critical temperaturewhichaisprescnibedfor centrifugalseparation. In Zthisipreferred'modification, an organic mixture .containing compounds that will complexwith :urea is contactedwith an aqueous saturated solution-or slurry ofurea. at; a temperature between "120 andl40 F. Whencomplex-formationjsefifeofiedrat a'temperaturefalling-within:the'critical temperature range, there .is no need fortern.- ;perature adjustment prior to or during centrif--.ugal--separation. Inany event, the-temperature is maintained below 150F. during complex formation.

AS indicated previously, the :process of .this ,invention :isparticularly.,applicable :to treating .gas oils-to produce .low pour:oils effective for cold weather-diesel operation and as a jet fuel. TheProcess of this invention is illustrated in .the Jill.- .lowing examplewherein a gas .oil having a :pour

of +25 F. is contacted with an aqueous slurry of urea whereby afterseparation of urea complex therefrom in accordance with the process ofthis invention there is formed a gas oil fraction having a pour of about20 F. Depending on the amount of urea employed, dewaxed oils of higheror lower pour can be obtained.

Example A a o having the .tcllomins properties is of waterper barrel ofgas oil at about F. The resulting mixture is stirred until the complexbetween the urea and wax components of the gas oi-ljs donned. Thetemperature is maintained at about 130 F. and the jnixture subjected tocon- .tinuous-centrifuging. Two streams areobtained, the -,dewaxed gasoil stream from the center .91 the centrifuge .and a water rich ,stream-contain ing complex and any excess .urea not .dissolved from theperiphery of the centrifuge. The .dewaxed gas oil amountsto83 percent ofthe ,charge gas oil and has a pour point of 20 F. andcetane number. of52.0.

The water rich streamcontainili theureawax complex and excessurea .isremoved Ifrom thepontinuous centrifuge as a slurry .and heated to about160 F. which causes the complex to deecompose andithe ureatodissolve.From .the heat .eX0.hanger the mixture' of moltenwaxanda .watersolutionof ,urea is gtakento .asettler. ,JIhe molten wax, removed,fromthetopof this settleramounts {to 1'7 per cent of the charge ,gasoiland iscompos d lm entirely of n mal paraffi dro- ;carbons. The ureawater solution is recycled and qontactedagain with freshgas oil.charge.

In the foregoingexample there. is described a. preferred. modification.of .the su ject invention wherein contact of the organic mixturewithurea aqueous medium is effected-eta temperature falling within the120-140 F; ,rangeprescribed ,for centrifugalseparation. It willberecognized that contact of urea and or anic mixture ,can; ,be eiiectedat temperatures below the prescribed separationrtemperature; -in.suchinstances, atem p crature adjustment is-required prior to centrii-'ugal-separation. v

Qbviousl-y, many modifications and vatiations of the inventionashereinbefore set forth may be made-without departing from the spiritand scope thereof, and-therefore-only such limitations should .beimposed as are indicated in the .appended claims.

We claim:

1. In a process involving-,formation of complexes comprising urea andorganic compounds containing ,a normal aliphatic chain of at least sixcarbon atoms by contacting aqueous ureaat a temperature below 150 :withamixturecontainingsaid com-pounds, said aqueous urea being selected fromthe group consisting ,of saturated zureasolution and'a urea slurry,theimprovement which comp i es efieo in s paration of id resultingcomplex-containing mixture consist- .ingof water and said organiccompounds bycent rifuging at .a temperature between 120 and F. wherebythere are obtained an organic light stream and a dense aqueous streamcontaining said complex.

2. A process according to claim 1 in which contact of urea with theorganic mixture is eifected at a temperature between 120 and 140 F.

3. In a process involving the formation of complexes comprising urea andnormal aliphatic hydrocarbons containing at least six carbon atoms bycontacting aqueous urea at a temperature below 150 F. with an organicmixture containing said aliphatic hydrocarbons, said aqueous urea beingselected from the group consisting of saturated urea solution and a ureaslurry, the improvement which comprises efiecting separation of saidresulting complex-containing mixture consisting of water and saidhydrocarbons by centrifuging at a temperature between 120 and 140 F.whereby there are obtained a light hydrocarbon stream and a denseaqueous stream containing said complex.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,499,820 Fetterly Mar. 7, 1950 2,557,257 Melrose June 19,1951 OTHER REFERENCES Bengen, Technical Oil Mission Reel 143, pages 2 to6, May 22, 1946.

1. IN A PROCESS INVOLVING FORMATION OF COMPLEXES COMPRISING UREA ANDORGANIC COMPOUNDS CONTAINING A NORMAL ALIPHATIC CHAIN OF AT LEAST SIXCARBON ATOMS BY CONTACTING AQUEOUS UREA AT A TEMPERATURE BELOW 150* F.WITH A MIXTURE CONTAINING SAID COMPOUNDS, SAID AQUEOUS UREA BEINGSELECTED FROM THE GROUP CONSISTING OF SATURATED UREA SOLUTION AND A UREASLURRY, THE IMPROVEMENT WHICH COMPRISES EFFECTING SEPARATION OF SAIDRESULTING COMPLEX-CONTAINING MIXTURE CONSISTING OF WATER AND SAIDORGANIC COMPOUNDS BY CENTRIFUGING AT A TEMPERAUTRE BETWEEN 120 AND 140*F. WHEREBY THERE ARE OBTAINED AN ORGANIC LIGHT STREAM AND A DENSEAQUEOUS STREAM CONTAINING SAID COMPLEX.